The present invention, in general, pertains to a method of and apparatus for automatically deriving range information. More particularly, it relates to a method of and apparatus for automatically establishing a plurality of range readings for different portions of a scene and for controlling photographic operations as a function of these readings.
In the photographic arts, various systems have been proposed for deriving range information usable for controlling photographic functions. Typically in such systems energy is transmitted to an object and the reflected energy is detected. Characteristics of the transmitted and reflected energy are contrasted for purposes of deriving a signal representative of the subject-to-system distance. The resultant range signal can be used for purposes of controlling such functions as focusing, flash firing and exposure.
One known ranging system of the above type utilizes acoustic pulses for determining the object-to-system distance. In this kind of autofocusing system, the elapsed time between transmission and receipt of an ultrasonic signal, which is bounced off the object, is utilized for deriving a range signal. This signal is usable for driving a lens element of a lens assembly to a correct focal position corresponding to the distance the object is from the camera so that such object may be properly focused. Commonly-assigned U.S. Pat. No. 4,199,246, entitled "Ultrasonic Ranging System for a Camera", is representative of such systems.
Another known ranging technique relies upon the concept of triangulation. An example of an active triangulation ranging system is employed in Canon's AF 35M camera. In this connection, an infrared-emitting diode shifts laterally, during a measuring cycle, relative to a fixed sensor cell which monitors the maximization of the reflected infrared radiation. The distance the emitter diode travels to provide such maximization is related to the subject distance. Correspondingly, a range signal is derived for adjusting focusing of a lens assembly.
Another known type of active triangulation system is that in which use is made out of a position sensitive photodetector. In such system, a ranging beam is aimed at the object of interest. The beam reflected from the object strikes the position sensitive photodetector and results in voltage outputs from opposite ends thereof. The voltage output ratio is proportional to object distance and can be converted into a ranging signal for control of, for instance, focusing.
There are other types of ranging systems employing triangulation, for instance, those disclosed generally in U.S. Pat. Nos. 3,736,057 and 4,150,888. The concept of triangulation is also employed in a passive type optical ranging system such as the type utilized in Honeywell's Visitronic system; and described basically in U.S. Pat. No. 3,945,023. This system compares the voltage outputs of two five-panel photosensor arrays. A moving mirror scans the image. The system includes two mirrors, one fixed and one movable. When the system's integrated circuit detects matching voltage patterns from both arrays, it can calculate the range for directing the lens element to the proper focal position corresponding to subject range.
The foregoing described autofocusing systems have improved significantly amateur photography. By providing for point-and-shoot photography, these autofocusing systems have eliminated what is for most people the hardest part of photography--focusing. While these systems have performed highly satisfactorily, they nonetheless have certain shortcomings. Most notably, each of the noted active systems requires that the source of transmitted energy be properly aimed at the object sought to be in-focus. Otherwise, of course, the resultant photograph will be out-of-focus. Aiming is made more difficult because the source of transmitted energy is normally a narrow beam. Thus, proper focusing is a function of rather precise aiming. Hence, it is not always achieved easily.
Furthermore, there are other limitations. For example, if one subject is in the foreground with another subject in the background, in all probability only one of the two subjects will be in-focus. Thus, these systems do not provide means for ranging which accommodates for scenes in which background and foreground subjects are at different distances. Moreover, the focusing is locked into the range signal generated by a single subject. This is limiting because photographers cannot focus closer than or beyond a subject of interest. While photographers have been known to focus closer than or beyond a subject of interest for depth of field purposes, such focusing is done manually. Commonly-assigned and copending application Ser. No. 244,964, filed Mar. 18, 1981, discloses a ranging system in which the objective lens is focused automatically to a point beyond the subject in accordance with available subject illumination.
From the above, it will be appreciated readily that known autofocusing systems provide extremely significant improvements over the more traditional methods of camera focusing, but they nevertheless are limited in several important respects as mentioned above.